1. Field of the Invention
The present invention relates to a paper making machine, and, more particularly, to a machine for the production of tissue paper.
2. Description of the Related Art
Many different types of production processes for tissue paper are known.
The expensive TAD method or the method described in PCT/EP2005/050203, for example, are used for the production of a particularly high-quality and fleecy tissue paper with a higher absorbency and high water absorption capacity coupled with high tear resistance. With the method described in PCT/EP2005/050203 the tissue paper web is formed in the forming section on a structured mesh and then dewatered in several dewatering steps under the action of pressure. For example, the tissue paper web is conveyed throughout the dewatering on the structured mesh on which it was formed. In this way a tissue paper with voluminous, less compressed areas, and with compressed solid areas, is formed. With the method described in PCT/EP2005/050203 an elongated nip is formed between the Yankee drying cylinder and a mating surface constructed as a shoe press unit. Thanks to the elongated nip a good transfer from the structured mesh to the Yankee drying cylinder is assured. Here the function performed by the elongated nip is solely to transfer the tissue paper web from the structured mesh to the Yankee drying cylinder. Therefore it would be desirable for the expensive shoe press unit to be replaced by a cheaper press roller. In tests, however, rollers with a solid circumferential surface display poor transfer properties of the tissue paper web from the mesh to the Yankee drying cylinder because a vacuum is generated in the opening nip and leads to the tissue paper web adhering to the mesh. A satisfactory transfer performance is obtained by way of bores in the cylindrical surface of the roller, but the roller casings, known from the prior art with their relatively large bores of more than 3.8 mm, leave unacceptable shadow marks on high-quality tissue paper.
A low production capacity is usually achieved with the above mentioned methods than with methods in which less high-quality, meaning less fleecy and less absorbent tissue papers are produced. Such a method is realized, for example, by way of a paper machine with a crescent arrangement in which the tissue paper web is formed in the forming section on a felt and is conveyed thereon up to the Yankee drying cylinder via an elongated nip formed between the Yankee drying cylinder and a shoe press unit. With this method the drying of the tissue paper web takes place, to an essential extent, in the elongated nip. With this method, too, there is a need, due to pressure from costs, to replace the expensive shoe press unit with a cheaper press roller. However, tests in this connection have shown that rollers with a solid circumferential surface and rollers with blind bores are not suitable for replacing the shoe press unit due to too low a dewatering performance.
Furthermore, manufacturers of tissue paper face changing requirements with regard to the quality and quantity of the tissue paper to be produced. For example, tissue paper manufacturers have to provide their customers periodically with high-quality fleecy tissue paper in small quantities and periodically with less high-quality tissue paper often in large quantities.
The provision of production machines for both methods is costly for the tissue paper manufacturer as this means on the one hand that both types of production machines have to be purchased and on the other hand that depending on the current market demands the one or other machine cannot be used for production.